Electrical machines, including, for example, electric motors and generators, generate heat that is often associated with electrical and mechanical losses within the machines. In rotating electrical machines losses are particularly high during starting or dynamic braking. The amount of heat generated by a particular electrical machine may depend on a variety of different factors, including, for example, the magnitude of the load on the electrical machine and the frequency of the starting and braking of the electrical machine, among other factors. Cooling of electrical machines is often necessary to continuously transfer the heat from the machine to mitigate a variety of heat-induced problems that may hinder the operation and/or shorten the life span of electrical machines, including short circuits and winding burnout and failure, among other heat related issues.
Cooling of electrical machines often involves transferring the heat generated by the machine to a cooling medium, such as air, for example. Conventionally, electrical machines are cooled externally from the outer surface of the housing enclosing the operational components of the machine, often by one or more fans mounted on the shaft of the machine. To allow for operation of the machine in either direction of rotation, the fans are usually of the bi-directional type and made of a strong plastic, aluminum, or steel material. However, such cooling methods require that the heat be conducted from the windings through the core yoke, core/housing shrink fit, and the wall of the housing. In certain machines, this heat flow path is not adequate to prevent overheating because the heat flux generated within the machine is too great to be removed via conduction through the cross-sectional area of the available heat flow path. Alternatively, the cooling medium may be flowed through the machine. However, such a cooling scheme requires power to generate an adequate cooling flow, which lowers the efficiency of the electrical machine. Moreover, such a cooling scheme requires cooling flow paths be formed through the machine, which inevitably include pressure losses and increase the complexity and cost of manufacturing the electrical machines. Accordingly, there remains a need for further contributions in this area of technology.